(a) Field of the Invention
The present invention relates to a scintillation camera, and more particularly, it pertains to a device for designating a region of interest for a scintillation camera.
(b) Description of the Prior Art
Scintigram-producing apparatuses intended for measuring and recording an image representing the distribution of a radioactive isotope administered in a human body, i.e. the so-called scintillation camera, are widely used in the medical field as a means for making a diagnosis of a patient. It has been the practice in scintillation cameras of the prior art to set a desired region within the visual field of the camera, and to measure the count of gamma rays which are incident onto this set region. A means for a discriminating the presence or absence of the incident gamma rays within the set region is called a device for setting a region of interest for scintillation camera.
In such a device for setting a region of interest for a scintillation camera, it is known to be desirable to insure an exact agreement between the set region and the configuration of the specific part of the organ which is the object of measurement.
Organs of human beings have configurations which are generally close to either a circle or an ellipse. Thus, for example, if the region which is set on the camera is rectangular, it is not possible to perform a correct setting of a region so as to be in conformity with the actual shape of the objective organ. The discrepancy which arises between the circular or elliptic shape of the organ and the rectangular region which is set for the camera will bring about a measurement error when comparison is made between the radiation intensities in the objective portion of the organ and the radiation intensities in the areas surrounding this objective portion. For example, let us assume that a rectangular region is set over a kidney which actually has a configuration resembling that of a broad bean. Then, the portion of the region occupied by the configuration of the kidney within the rectangular region will be of the order of only 70-80% at the greatest. The remaining 30-20% portion is located outside the boundary of the kidney. The radiation intensities in those regions located outside the kidney are low. Thus, there arises a substantial error or discrepancy between the total count of the mean radiation intensity of gamma rays located within the rectangular region and the actual total count of the mean radiation intensity of gamma rays in the region of the kidney.
A major problem which is encountered in known devices for setting a region of interest for a scintillation camera is that it is not possible to set a region for the scintillation camera in a manner faithful to the actual selected portion of the given organ, and that accordingly there arises a discrepancy between the value of measurement and the actual count of gamma rays.